Test composition for determining the concentration of quaternary ammonium compounds in aqueous solution



United States P 6 1 OF TEST COMPOSITION FOR DETERMINING THECONCENTRATION OF QUATERNARY AMMO- NIUM COMPOUNDS IN AQUEOUS SOLUTIONMorris E. Anerbach, Albany, and Robert S. Browning, Schodack, N.Y.,assignors to Sterling Drug Inc., New York, N.Y., a corporation ofDelaware No Drawing. Filed Apr. 19, 1960, Ser. No. 23,146 a p scram. or.252-408) This invention relates to a novel chemicalcomposition usefulfor determination of the concentration of quaternary ammonium compoundsin'solution, particularly for distinguishing between aqueous solutionscontaining different small concentrations of quaternary ammoniumcompounds.

Manyv surface-active quaternary ammonium compounds have valuableantibacterial properties which adapt them to wide use as sanitizing anddisinfecting agents, for instance in washing and rinsing a wide varietyof articles which come into contact with food, such as eating anddrinking utensils, dairy equipment, counter tops, brewing equipment, andthe like. For such purposes, these compounds are ordinarily employed indilute aqueous solutions, usually in a concentration of about onepercent or less by weight. In 'a given use, conventionally a minimumrequired strength of the particular quaternary ammonium compoundsinvolved is recommended by the manufacturer, and in some instancesFederal and State regulations may specify minimum effectiveconcentrations. As is well known, during. use of these aqueous solutionstheir bactericidal potency may be diminished by dilution, or thequaternary ammonium compounds therein may interact with agents in ,suchmanner as to reduce or destroy the antibacterial activity. Consequently,in order to ensure against use of, solutions of inadequate strength,especially when repeated' use is involved, it is highly desirable tohave available a simple means for determining routinely whether or notthe effective quaternary ammonium concentration at any particularstage'of use is below the minimum standard. Various test procedures havebeen employed for this purpose, but some of these require skilledtechnicians and are thus unsuited to routine field use, and the available simple tests have one or more' undesirable features such asinconvenience,v unreliability, or production of results which areditficult to interpret.

. fonated amides and amines, for instance sodium lauryl sulfate, sodiumlauryl sulfonate, sodium myristyl sulfonate, di-(higher alkyl)alkalimetal sulfosuccinates such' as the dioctyl sodium sulfosuccinates,sodium p-dodecylbenzenesulfonate, the sodium salt of N-methyl-N-(Z-sulfoethyD-oleic amide, sulfonated polyethanolamine, and the like. Weparticularly prefer sodium lauryl sulfate and the dioctyl sodiumsulfosuccinates, for example bis- (2-ethylhexyl) sodium sulfosuccinate.

Our new chemical composition is readily prepared using conventionalblending and mixing techniques, for example by homogeneously mixingtogether appropriate amounts of the anionic detergent, methyl orange,and bromophenol blue. The resulting reagent mixture can be used assuch'or, if desired, suitable solvents or tabletting excipients areadded before, during, or after the mixing operation.

When the new composition of this invention is added to an aqueousquaternary ammonium antibacterial solution, the anionic detergentcomponent of our composition reacts stoichiometrically with thequaternary ammonium compound to form a non-ionized salt, and the mixtureof dyes imparts to the solution a distinctive and characteristic colorwhich is indicative of whether there is an excess of the anionicdetergent or the quaternary ammonium compound in the reaction mixture.Thus, when there is an excess of the anionic detergent in the reactionmixture, the mixture of dyes colors the solution reddishbrown; and whenthere is an excess of the quaternary ammonium compound, the dyesinteract with this excess to form a combination of complex compoundswhich colors the solution bluish-green. The distinction between point issharp and the appearance of in-between shades which might confuse theobserver in border-line cases It is therefore a primary object of thisinvention to provide simple and convenient means, for'determ'iningrapidly and reliably whether dilute aqueous solutions of anantibacterial quaternary ammonium compound contain an adequate effectiveconcentration of the said compound. This obiect has been accomplished byaffording in the present invention a novel chemical composition usefulfor distinguishing visually between solutions containing at least apredetermined level of concentrationoi a quaternary ammonium compoundand solutions containing less than the predetermined level.

The new chemical composition of the instant inven tion for testingdilute aqueous solutions of quaternary ammonium compounds comprises areagent mixture consisting essentially of methyl orange and bromophenolblue, in approximate weight ratio to each other of three is minimized.

It will be appreciated that it is the effective quaternary ammoniumconcentration in the solution which is measured by use of ourcomposition, and there is no interference with the test procedure by anyportion of the quaternary ammonium compound which may have'been removedfrom solution prior to the test, for instance by precipitation ofsolution in water-insoluble form by interaction withsoaps or anionic'wetting agents.

The combined proportion by weight of the methyl orange and bromophenolblue constituents with respect to the total weight of the essentialingredients of the reagent mixture, namely methyl orange, bromophenolblue, and anionic detergent, is in the range from approximately 8percent up to approximately 35 percent. A weight ratio of at leastapproximately three parts of methyl orange to one part of bromophenolblue is preferred, since this ,afiords the optimum sharpness ofdifferentiation between the colors produced on each side of theend-point. Slight variations from the three to one ratio-can be made,however, without substantial adverse efiect on the colorditferentiation.

The proportion by weight of the anionic detergent constituent withrespect to the total weight of the essential ingredients of the reagentmixture, namely methyl orange, bromophenol blue and anionic detergent,is in the range from approximately 92' percent down to approximately 65percent. As will be appreciated from/the considerations set forthhereinbelow, the weight of the anionic detergent in any given quantityof our new composition must be accurately known. This object is ofcourse readily attained by using a known weight of the anionicdetergent, homogeneously distributing the anionic detergent throughoutour composition, and determining the final weight of the homogeneouslymixed composition, so that the weight of the anionic detergent per unitweight of the composition can be calculated.

The preferred ranges of proportions of the ingredients in the reagentmixture are 20-30 percent by combined weight of the two dyes and 80-70percent of the anionic detergent.

When the molecular weight of the quaternary ammonium compound (or themean molecular weight in the case of a mixture of quaternary ammoniumcompounds) is known, our new composition can be employed to determinewhether more or less than a predetermined quan tity of the quaternaryammonium compound or compounds is present in a given volume of anaqueous solution. Thus, by adding a quantity of our new compositioncontaining a known weight of the. anionic detergent to a test sample ofthe quaternary ammonium solution, it is rapidly and convenientlyascertained by observation of the resulting color whether the amount ofquaternary ammonium compound in the test sample was above or below theamount necessary to interact stoichiometrically with the weight of theanionic detergent employed; and also of course, when a measured volumeof the test sample is employed, it is ascertained at the same time bythis test whether the concentration of the quaternary ammonium compondis above or below a calculated value. Further, by adding, to each ofseveral samples of the quaternary ammonium solution having the samevolume, quantities of our composition containing the anionic detergentin different, known weight for each sample, or alternatively and moreconveniently by adding to each of several test samples of the quaternaryammonium solution having different, known volumes a quantity of ourcomposition containing the anionic detergent in the same weight for eachsample, a rapid approximation of the effective concentration of thequaternary ammonium compound can be made when appropriate selections ofthe weights of reagent and volumes of test samples have been made, asillustrated below in the examples. If a more exact determination of theconcentration of the quaternary ammonium compound is desired, thequaternary ammonium solution can be titrated against an aqueous solutionof our composition containing a known concentration of the anionicdetergent.

For use in field tests of quarternary ammonium solutions to determinewhether minimum concentration requirements are met, the use of tabletshas a number of obvious advantages, and we therefore prefer to employsolid anionic detergents in making and using embodiments of ourinvention. The composition is advantageously tabletted in such mannerthat the weight of the anionic detergent component in one tablet isstoichiometrically equivalent to the amount of a given quaternaryammonium compound contained in a convenient selected volume of thesolution to be tested when the solution is at the recommended minimumconcentration level.

We have found that our invention is particularly adapted to the testingof aqueous solutions containing N-higher alkyl-N,N-di-loweralkyl-N-benzylammonium salts, particularly the higheralkyl-dimethyl-benzyl-ammonium halides, such as benzalkonium chloride,having a mean molecular weight of 357 and represented by the structuralformula CHI CH! quaternary ammonium compound at the commonly usedconcentration of 200 p.p.m. For instance, when benzalkonium chloridesolutions at a minimum recommended level of 200 p.p.m. are to be testedand the volume of the test sample is conveniently selected at 8 ml., weprefer that each tablet of our composition contain 1.29 mg. of sodiumlauryl sulfate (molecular weight: 288), the amount of the latterrequired to react with the 1.60 mg. of the quaternary ammonium compoundpresent in 8 ml. of a 200 p.p.m. solution.

Even when tablets of our composition are designed especially ,for usewith a particular quarternary ammonium compound or for a given minimumuse concentration of the quaternary ammonium compound, the same tabletscan also be used conveniently for testing other quaternary ammoniumcompounds or for other minimum use concentrations by an appropriateselection of the volume of the test solution or by appropriate dilutionof a measured volume of the test sample with a, known volume of waterbefore the test is made, as illustrated in Examples 2 and 4 hereinbelow.

Our invention is illustrated by the following examples without, however,being limited thereto. In these examples, in each instance the termparts is employed to indicate parts by weight. 7

Example I A. 129 parts of sodium lauryl sulfate, 30.0 parts of methylorange, and 10.0 parts of bromophenol blue were mixed and groundtogether thoroughly to form a uniformly blended homogeneous powder. Thesuitability of the composition thus obtained as a reagent was tested inthe following manner. In wide variety of antibacterial applications, aminimum concentration of benzalkonium chloride in water of 0.02 percent,or 200 p.p.m. (parts per million) is recommended. Accordingly,standardized aqueous solutions containing respectively 100 p.p.m., 150p.p.m., 200 p.p.m., and 250 p.p.m. of benzalkonium chloride wereprepared. An ml. sample of each solution was'placed in respective testtubes, and to each of the four tubes there was added 16.9 mg. of theblended powder prepared as described. The tubes were agitated tofacilitate solution, and in each instance all of the powder dissolvedwithin a minute or less. The

color of each solution was then observed, as follows: in the two tubescontaining the solutions in which the concentration of benzalkoniumchloride was ppm. and p.p.m. respectively, the color was reddish-brown;at 200 ppm. of benzalkonium chloride, the color was brown; and at 250ppm. of benzalkonium chloride, the color was bluish-green.

B. The reagent composition prepared as described in part A was alsofound to be fully satisfactory in field tests under actual conditions ofuse. Thus, an aqueous solution containing slightly more than 200' p.p.m.of benzalkonium chloride was used repeatedly as a sanitizing rinse forglassware... After each such rinsing operation, a sample of the solutionwas tested with the reagent composition described above in partA. Thecolor of the resulting test solutions was bluish-green in eachsuccessive test until a reddish-brown test solution indicated that thebenzalkonium chloride concentration had dropped below the recommendedsafe minimum of 200 p.p.m.

a,979,4es

129 parts of sodium lauryl su1fate, 30 parts of methyl orange, parts ofbromophenol blue, 14,945 parts of lactose, 800 parts of starch, and 80parts of magnesium stearate were mixed and ground together to produce auniformly blended homogeneous, powder. This powder was then tabletted toproduce tablets weighing 160 mg. each which contained, as the essentialactive ingredients thereof, 1.29 mg. of sodium lauryl sulfate, 0.3 mg.of methyl orange, and 0.1 mg. of bromophenol blue per tablet.

We found that these tablets were especially convenient for use in fieldtests of aqueous quaternary ammonium solutions. Thus, by placing one ofthese tablets in an 8 ml. sample of an aqueous solution of benzalkoniumchloride, there was obtained a very rapid indication of whether thesolution was at the recommended level of 200 p.p.m. or above, asevidenced by a bluish-green color, or was below the level of 200 p.p.m.,as evidenced by a reddish-brown color. When desired, the testing of thesolutions which had a reddish-brown color was readily extended to obtainan estimate of how much below the recommended minimum the concentrationof benzalkonium chloride was. This was done by adding further incrementsof the solution being tested. Thus, if the color shifted fromreddish-brown to bluish-green on addition of 1 ml. more of the solution,this indicated a benzalkonium chloride concentration of at least 178p.p.m., and of course below 200 p.p.m. If the color did not shift afteraddition of the 1 ml. portion of solution, but did shift to bluish-greenafter adding a second 1 ml. portion of solution, this indicated abenzalkonium chloride concentration of at least 160 p.p.m., and ofcourse below 175 p.p.m. The testing of solutions below the 160 p.p.m.level can be extended as desired by addition of further increments ofsolution until a shift in color from reddish-brown to bluish-green isobtained.

For certain applications, the recommended concentration of benzalkoniumchloride is greater than 200 p.p.m. These stronger solutions were testedwith the above tablets by diluting the solution with the amount of watercalculated to reduce the benzalkonium chloride to 200 p.p.m., thentesting an 8 ml. sample of the diluted solution with one reagent tableas above described, and finally multiplying the indicated concentrationby the dilution factor to obtain the concentration of the originalsolution. For example, one ounce of a benzalkonium chloride solutionwhich should be used at a minimum concentration of 1600 p.p.m. wasdiluted with seven ounces of water, the reagent tablet was added to an 8ml. sample of the resulting solution, and the found concentration valuewas multiplied by eight to obtain the concentration of the originalsolution.

Example 3 To prepare a composition like that described in part A ofExample 1 but containing an equivalent amount of dioctyl sodiumsulfosuccinate (molecular weight 444) as the anionic detergent, the 129parts of sodium lauryl sul the 8 ml. sample used for benzalkoniumchloride, so that otherwise the testing procedure and the reading andinterpretation of results could then be carried out exactly as in thecase of benzalkonium chloride described above. The calculation is asfollows.

Molecular weight of QAC v357 Thus, in testing solutions oflauryl-dimethyl-benzyl-ammonium chloride, having a molecular weight of339.5, to determine deviations from a recommended use level of 200p.p.m., the volume of test sample employed was 8=the test volume of QAC430.5 rgg XS-QJ ml.

Example 5 Following the procedure of Example 2, but using 404 parts ofsodium lauryl sulfate instead of 129 parts, there 7 were obtainedtablets weighing about 163 mg. each which mg. of methyl orange, and 0.1mg. of bromophenol blue per tablet.

Example 4 The 160 mg. tablets described in Example 2 were also usedconveniently and satisfactorily to test solutions of quaternaryammoniumcompounds other than benzalkocontained, as the essential activeingredients thereof, 4.04 mg. of sodium lauryl sulfate, 0.3 mg. ofmethyl orange, and 0.1 mg. of bromophenol blue per tablet. Each of thesetablets had the calculated amount of sodium lauryl sulfate to interactstoichiometrically with the amount of benzalkonium chloride contained in5 m1. of an aqueous solution containing 1000 p.p.m. of the quaternary.These tablets were found to be highly useful for the testing of 5 ml.samples of aqueous benzalkonium chloride solutions for deviation fromrecommended use concentration of 1000 p.p.m.

We claim:

1. A chemical composition for testing the concentration of diluteaqueous solutions of quaternary ammonium compounds which comprises areagent mixture homogeneously distributed in said composition andconsisting essentially of methyl orange and bromophenol blue, inapproximate weight ratio to each other of three to one respectively,andan anionic detergent of the group consisting of water-soluble syntheticorganic sulfate and sulfonate anionic detergents, the combinedpercentage by weight of the methyl orange and the bromophenol blue insaid reagent mixture being in the approximate range 8-35 and thepercentage by weight of the said anionic detergent in the reagentmixture being in the approximate range 92-65.

2. A chemical composition for testing the concentration of diluteaqueous solutions of quaternary ammonium compounds which comprises areagent mixture homogeneously distributed in said composition andconsisting essentially of methyl orange and bromophenol blue, inapproximate weight ratio to each other of three to one respectively, andsodium lauryl sulfate, the combined percentage by weight of the methylorange and the bromophenol blue in said reagent mixture being in theapproximate range 8-35 and the percentage by weight of the sodium laurylsulfate in the reagent mixture being in the approximate range 92-65.

3. A chemical composition for testing the concentra tion of diluteaqueous solutions of quaternary ammonium compounds which comprises areagent mixture homogeneously distributed in said composition andconsisting essentially of methyl orange and bromophenol blue, inapproximate weight ratio to each other of three to one respectively, andsodium lauryl sulfate, the combined percentage by weight of the methylorange and the bromophenol blue in said reagent mixture being in theapproximate range 20-30 and the percentage by weight of the I sodiumlauryl sulfate in the reagent mixture being in the approximate range80-70.

4. A chemical composition for testing the concentraapproximate weightratio to each other of three to one respectively, and dioctyl sodiumsulfosuccinate,- the combined percentage by weight of the methyl orangeand the bromophenol blue in said reagent mixture being in theapproximate range 8-35 and the percentage by weight of the dioctylsodium sulfosuccinate in the reagent mixture. being in the approximaterange 92-65.

5. A chemical composition for testing the concentration of diluteaqueous solutions of quaternary ammonium compounds which comprises areagent mixture homogeneously distributed in said composition andconsisting essentially of approximately one part by weight ofbromophenol blue, approximately three parts by weight of methylorange,and approximately thirteen parts by weight of sodium lauryl sulfate.

6. A chemical composition for testing the concentration of diluteaqueous solutions of quaternary ammonium compounds which comprises areagent mixture homogeneously distributed in said composition andconsisting essentially of approximately one part by weight ofbromophenol blue, approximately three parts by weight of methyl orange,and approximately forty parts by weight of sodium lauryl sulfate.

7. A reagent tablet for testing the concentration of dilute aqueoussolutions of quaternary ammonium compounds comprising in dry,homogeneous admixture the following ingredients: 1.29 mg. of sodiumlauryl sulfate; approximately 0.1 mg. of bromophenol blue; approximately0.3 mg. of methyl orange; approximately mg. of lactose; approximately 8mg. of starch; and approximately 0.8 mg. of magnesium stearate.

8. A reagent tablet for testing the concentration of dilute aqueoussolutions of quaternary ammonium compounds comprising in dry,homogeneous admixture the following ingredients: 4.04 mg. of sodiumlauryl sulfate; approximately 0.1 mg. of bromophenol blue; approximately 0.3 mg. of methyl orange; approixmately 150 mg.

of lactose; approximately 8 mg. of starch; and approximately 0.8 mg. ofmagnesium stearate.

References Cited in the file of this patent UNITED STATES PATENTSConklin June 10, 1952 OTHER REFERENCES

1. A CHEMICAL COMPOSITION FOR TESTING THE CONCENTRATION OF DILUTEAQUEOUS SOLUTIONS OF QUATERNARY AMMONIUM COMPOUNDS WHICH COMPRISES AREAGENT MIXTURE HOMOGENEOUSLY DISTRIBUTED IN SAID COMPOSITION ANDCONSISTING ESSENTIALLY OF METHYL ORANGE AND BROMOPHENOL BLUE, INAPPROXIMATE WEIGHT RATIO TO EACH OTHER OF THREE TO ONE RESPECTIVELY, ANDAN ANIONIC DETERGENT OF THE GROUP CONSISTING OF WATER-SOLUBLE SYNTHETICORGANIC SULFATE AND SULFONATE ANIONIC DETERGENTS, THE COMBINEDPERCENTAGE BY WEIGHT OF THE METHYL ORANGE AND THE BROMOPHENOL BLUE INSAID REAGENT MIXTURE BEING IN THE APPROXIMATE RANGE 8-35 AND THEPERCENTAGE BY WEIGHT OF THE SAID ANIONIC DETERGENT IN THE REAGENTMIXTURE BEING IN THE APPROXIMATE RANGE 92-65.